The present disclosure relates to an image forming apparatus that uses a detachable fixing unit that fixes toner by heating paper after a toner pattern is transferred.
In an image forming apparatus such as a printer and the like, an image pattern that is composed of toner is first formed on a photosensitive drum, and after this image pattern is transferred to paper (a medium), the image pattern is fixed to the paper by a fixing roller that is maintained at a high temperature. When doing this, fixing the toner to the paper is performed while the paper is nipped and conveyed between a fixing roller and pressure roller. Degradation of the fixing roller and the like may occur over time, or paper may become jammed inside the fixing unit (paper jam may occur). Therefore, the fixing roller and the pressure roller are provided inside a fixing unit, and the fixing unit is normally configured so that the fixing unit can be attached to or detached from the main body of the image forming apparatus, and so that the work of attaching or detaching the fixing unit can be performed easily by a user.
In the fixing unit, in order to stably perform a fixing operation such as described above, normally a specified pressure is set to be applied between the pressure roller and the fixing roller. However, the fixing unit is configured so that when handling in case of the occurrence of a paper jam such as described above, or in order to perform various kinds of maintenance, a state can be set in which this pressure is greatly reduced from the normal pressure (released-pressure state). Moreover, a heater, a temperature sensor and the like are provided in the fixing roller in order to maintain the temperature of the fixing roller within a specific high-temperature range, and a connector for supplying electric power to the heater, temperature sensor and the like, or for exchanging electric signals between them is provided between the fixing unit and the main body.
In addition, the fixing roller and the like in the fixing unit may be mechanically driven from the main body side. Furthermore, switching states (normal state, released-pressure state) between the fixing roller and the pressure roller as described above may be performed by a motor for switching the pressure that is provided on the main body side. In order to properly operate this kind of fixing unit, it is necessary that the fixing unit be attached properly to the main body. When a user operates the image forming apparatus in a state in which this fixing unit is not attached properly (incomplete state), the alignment between the main body side and the fixing unit side of the image forming apparatus is lost. Therefore, image defects, paper jams, and the like may occur, and furthermore, damage to the fixing unit or the main body of the image forming apparatus may occur.
Therefore, the image forming apparatus is configured so as to recognize whether or not the fixing unit is attached properly to the main body, and when the fixing unit is not attached properly, disables operation of the image forming apparatus. Various kinds of sensors are necessary in order to determine whether or not the fixing unit is attached properly. However, in a typical image forming apparatus, sensors that are originally provided for other purposes are also used for determining whether or not the fixing unit is attached properly.
More specifically, sensors for this purpose, a pressure-release sensor (pressure-release-detection flag) and a fixing-conveyance sensor (transfer-material-detection flag) are used. The pressure-release sensor detects the state of the pressure between the fixing roller and the pressure roller (normal state (high pressure), released-pressure state (low pressure)). The fixing-conveyance sensor detects when the paper passes between the fixing roller and the pressure roller.
Specifically, the pressure-release sensor is an optical sensor that rotates according to change in the state between the fixing roller and pressure roller such as described above, and in the normal state detects that light is transmitted, and in the released-pressure state, detects that light is blocked.
The fixing-conveyance sensor, in order to determine whether or not the fixing operation on the paper is complete, detects whether or not the paper is directly below the fixing roller and the pressure roller. As the fixing-conveyance sensor an optical sensor that is the same as the pressure-state sensor is used. The sensor is set so that when there is paper (when the fixing operation is being performed), the sensor detects that light is transmitted, and when there is no paper (the fixing operation is finished), the sensor detects that light is blocked.
In this way, neither the pressure-release sensor nor the fixing-conveyance sensor is originally provided for determining whether or not the fixing unit is attached properly. However, a typical image forming apparatus is structured so that these sensors can also be used in determining whether or not the fixing unit is attached properly, and the pressure-release sensor and the fixing-conveyance sensor are provided at positions that are separated from each other. Therefore, at each location, it is particularly possible to determine whether or not the positional relationship between the fixing unit and the main body is proper. Consequently, it is not necessary to provide a new sensor for determining whether or not the fixing unit is attached properly, and so the image forming apparatus can be made inexpensively.
When the pressure-release sensor and the fixing-conveyance sensor are set as described above, and when both the pressure-release sensor and the fixing-conveyance sensor are in a state in which light is blocked, it is determined that the fixing unit is attached properly. Moreover, when one of the pressure-release sensor and the fixing-conveyance sensor is in a state in which light is transmitted, it is determined that the fixing unit is not attached properly on the side of that sensor. Furthermore, when both sensors are in a state in which light is transmitted, it is determined that the fixing unit is not attached properly on either side.